Ba x Sr (1-x) TiO 3 (BST) thin films are in situ deposited on a Ti matrix through the micro-arc oxidation technique, using a mixed aqueous solution of Ba(OH) 2 •8H 2 O, Sr(OH) 2 •8H 2 O and 0.05 M EDTA as the electrolyte. The influence of the Ba 2+ /Sr 2+ ratio on the phase composition, microstructure and properties of the BST thin films is investigated. Ba 0.6 Sr 0.4 TiO 3 , Ba 0.5 Sr 0.5 TiO 3 , and Ba 0.4 Sr 0.6 TiO 3 thin films have a cubic phase, while Ba 0.8 Sr 0.2 TiO 3 and Ba 0.7 Sr 0.3 TiO 3 thin films have a tetragonal phase. When the concentration of Ba 2+ in the electrolyte surpasses that of Sr 2+ , the width of micro-arc holes and the surface roughness of the film grow as the Ba 2+ concentration rises. Furthermore, the dielectric and ferroelectric properties of BST films are favorably connected with the surface morphology. When the Ba 2+ concentration is 0.06 M, the film has the best compactness and smoothness. In addition, the highest capacitance and lowest dielectric loss are achieved.